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Research Papers

Improving Efficiency of a High Work Turbine Using Nonaxisymmetric Endwalls—Part II: Time-Resolved Flow Physics

[+] Author and Article Information
P. Schüpbach1

Department of Mechanical and Process Engineering, LEC, Laboratory of Energy Conversion, ETH Zurich, 8092 Zurich, Switzerlandschuepbach@lec.mavt.ethz.ch

R. S. Abhari

Department of Mechanical and Process Engineering, LEC, Laboratory of Energy Conversion, ETH Zurich, 8092 Zurich, Switzerland

M. G. Rose

Institute of Aeronautical Propulsion, University of Stuttgart, 70569 Stuttgart, Germany

T. Germain, I. Raab, J. Gier

 MTU Aero Engines GmbH, Dachauer Strasse 665, 80995 München, Germany

1

Corresponding author.

J. Turbomach 132(2), 021008 (Jan 12, 2010) (10 pages) doi:10.1115/1.3103926 History: Received July 09, 2008; Revised January 27, 2009; Published January 12, 2010; Online January 12, 2010

This paper is the second part of a two part paper that reports on the improvement of efficiency of a one and a half stage high work axial flow turbine. The first part covered the design of the endwall profiling, as well as a comparison with steady probe data; this part covers the analysis of the time-resolved flow physics. The focus is on the time-resolved flow physics that leads to a total-to-total stage efficiency improvement of 1.0%±0.4%. The investigated geometry is a model of a high work (Δh/U2=2.36), axial shroudless HP turbine. The time-resolved measurements have been acquired upstream and downstream of the rotor using a fast response aerodynamic probe (FRAP). This paper contains a detailed analysis of the secondary flow field that is changed between the axisymmetric and the nonaxisymmetric endwall profiling cases. The flowfield at the exit of the first stator is improved considerably due to the nonaxisymmetric endwall profiling and results in reduced secondary flow and a reduction in loss at both hub and tip, as well as a reduced trailing shed vorticity. The rotor has reduced losses and a reduction in secondary flows mainly at the hub. At the rotor exit, the flow field with nonaxisymmetric endwalls is more homogenous due to the reduction in secondary flows in the two rows upstream of the measurement plane. This confirms that nonaxisymmetric endwall profiling is an effective tool for reducing secondary losses in axial turbines. Using a frozen flow assumption, the time-resolved data are used to estimate the axial velocity gradients, which are then used to evaluate the streamwise vorticity and dissipation. The nonaxisymmetric endwall profiling of the first nozzle guide vane show reductions in dissipation and streamwise vorticity due to the reduced trailing shed vorticity. This smaller vorticity explains the reduction in loss at midspan, which is shown in the first part of the two part paper. This leads to the conclusion that nonaxisymmetric endwall profiling also has the potential of reducing trailing shed vorticity.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Secondary flow model by Schlienger (4)

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Figure 2

Illustration of geometrical relations

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Figure 3

Total pressure at traverse plane S1ex

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Figure 4

Time-space diagram: pitch angle at traverse plane S1ex

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Figure 5

Time-space diagram: total pressure at traverse plane S1ex

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Figure 6

Time-space diagram: relative total pressure at traverse plane S1ex

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Figure 8

Time-space diagram: relative total pressure at traverse plane R1ex

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Figure 11

Pitch angle at traverse plane R1ex

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Figure 12

Total pressure at traverse plane R1ex

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Figure 13

Illustration for circumferential interpolation

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Figure 14

Time-averaged streamwise vorticity in the stator frame of reference at traverse plane S1ex (1/s)

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Figure 15

Time-averaged streamwise vorticity in the rotor frame of reference at traverse plane R1ex (1/s)

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Figure 16

Time-averaged D parameter in the stator frame of reference at traverse plane S1ex (%/s)

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Figure 17

Time-averaged D parameter in the rotor frame of reference at traverse plane R1ex (%/s)

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Figure 7

Relative total pressure at traverse plane R1ex

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Figure 9

Time-space diagram: rms of the total pressure random part at traverse plane R1ex (Pa)

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Figure 10

rms of the total pressure random part at traverse plane R1ex (Pa)

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